The primary objective of the proposed research is to further our understanding of the causes and consequences of individual differences in blood pressure (BP) dipping during nighttime sleep. Growing evidence indicates that elevated nighttime BP is superior to either clinic BP or daytime ambulatory BP as a prognostic indicator of cardiovascular morbidity and mortality. Blunted BP dipping favors the development of concentric left ventricular hypertrophy (LVH), a geometric restructuring of the heart that is often evident early in hypertension. LVH is the strongest known predictor of cardiovascular morbidity and mortality, other than advancing age. [unreadable] [unreadable] Despite compelling evidence for the pathophysiological consequences of blunted BP dipping, its biobehavioral determinants remain to be defined. The proposed study will evaluate several likely mechanisms of blunted BP dipping, including: (i) Sleep Quality; (ii) Psychosocial Stress; (iii) Sympathetic nervous system (SNS) activity, as well as: (iv) Vascular disease, in 200 men and women with high normal BP or Stage 1 hypertension. In addition, this study will characterize BP dipping in terms of the underlying hemodynamic mechanisms by supplementing 24-hour ambulatory BP monitoring with concurrent monitoring of cardiac output (CO) and systemic vascular resistance (SVR).The study will include a focus on African American ethnicity, and on menopause in women, because they are established risk factors for LVH. These factors are also related to blunted BP dipping, and to the biobehavioral mechanisms of BP dipping that we propose to assess. By defining the factors responsible for individual differences in BP dipping, the proposed research will yield information that should facilitate the development of effective biobehavioral interventions (e.g., pharmacological therapy, sleep therapy, stress management training) aimed at optimizing nighttime BP, and reducing cardiovascular disease risk.